Protection of low carbon steel in phosphoric acid by potassium iodide

Abstract

The corrosion of low carbon steel in 2.5 M phosphoric acid at temperature range of 30–60°C in presence and absence of potassium iodide as an inorganic inhibitor in the range of 0.02–0.05 M at static condition has been investigated. Weight loss and polarization techniques were employed in this investigation. The maximum value of inhibitor efficiency obtained was 99.95% at 50°C in presence of 0.05 M inhibitor concentration. The fraction of surface covered calculated from corrosion rates followed the Langmuir adsorption isotherm. Polarization experiments showed that for a given temperature, the curves were shifted towards the potential axis leading to lower the corrosion rates as the inhibitor concentration increased. Potassium iodide inhibits carbon steel corrosion in H3PO4 acid by affecting both anodic and cathodic partial reactions with the anodic reaction being more prevailing.